In a machine tool, for example, when an automobile part is subjected to cutting machining, a cutting fluid is supplied, and there is a method of MQL (Minimum Quantity Lubrication), which reduces a quantity of this cutting fluid to a necessary minimum. When the misty cutting fluid is supplied by the MQL, the quantity of the used cutting fluid is smaller, which brings about various advantages such as decrease in environmental load and reduction in cost. Accordingly, in the MQL, it is preferable that the supplied quantity of the cutting fluid is as small as possible.
On the other hand, it is preferable to sufficiently supply the cutting fluid in view of tool life and machining accuracy. Therefore, during machining by the MQL, the misty cutting fluid (hereinafter, the misty cutting fluid is referred to as “mist”) needs to be supplied efficiently and stably in the vicinity of a tool and at a portion where the tool and a workpiece come into contact with each other.
For this purpose, a state and a quantity of the mist ejected from oil holes in the vicinity of the tool, for example, oil holes provided in a drill itself need to be automatically measured and fed back to the machine tool to eject the mist without excess and deficiency.
In this case, it is convenient to visually confirm the quantity of the mist by the human eye, so that the ejection state of the mist can be checked at a glance.
However, the quantity of the mist, which is very small, cannot be visually confirmed as it is. Even if the ejected quantity of the cutting fluid is measured by a scale on a clear tube in which the cutting fluid is stored before the ejection, fine detection cannot be performed because of a very small consumed quantity of the mist. Moreover, when there occurs an ejection failure such as liquefaction of the mist, a reduction in the mist quantity in the clear tube and an actual mist quantity do not coincide with each other.
Furthermore, in view of automatization of a cutting machining facility, it is expected to automatically detect the quantity of the mist and automatically adjust the quantity of the mist based on this detected quantity so as to prevent the ejection failure.
Patent Literature 1 proposes a method for controlling a quantity of coolant in which a magnetic sensor is disposed in an outer peripheral portion of a body made of a non-magnetic material and a passage of a coolant is provided inside the body, so that a flow state of the misty coolant containing a magnetic fluid is detected by the magnetic sensor to control a quantity of the coolant based on this detected output.
Patent Literature 2 proposes an apparatus that optically detects a proportion of aerosol (mist), and gravimetrically detects a flow rate of a lubricant film precipitated inside the passage through which the aerosol passes to thereby measure the aerosol and the flow rate of the lubricant in the precipitated state, separately. In this optical sensor, there are two types: one is a type in which appropriate light is directed to the flow of the aerosol inside the measuring apparatus, and the other is a type in which an air flow is produced from the measuring apparatus to the optical sensor, and the aerosol is carried by the air flow.
Patent Literature 3 proposes a lubricant-ejection-state detecting apparatus for machine tool in which light of a projector is projected to an ejection point of a misty lubricant to detect a transmissivity determined by concentration of an ejection state in a light receiver, and a lubricant-ejection-state detecting apparatus for machine tool in which light of a projector is projected to an ejection point of a misty lubricant to detect reflected light from the misty lubricant in a light receiver. In each of these apparatuses, since the transmitted light or the reflected light of the misty cutting fluid is received by the light receiver, the projector, the ejection point and the light receiver are linearly located.